summarize the pertinent information obtained by applying the graphing strategy and sketch the graph of…

summarize the pertinent information obtained by applying the graphing strategy and sketch the graph of f(x)=2(4 - x)e^x. find the intervals where f(x) is concave upward or downward. select the correct choice below and fill in the answer box(es) to complete your choice. a. the function is concave upward on . it is never concave downward. (type your answer in interval notation. use a comma to separate answers as needed.) b. the function is concave upward on . it is concave downward on . (type your answers in interval notation. use a comma to separate answers as needed.) c. the function is concave downward on . it is never concave upward. (type your answer in interval notation. use a comma to separate answers as needed.)
Answer
Explanation:
Step1: Find the first - derivative
Use the product rule $(uv)' = u'v+uv'$, where $u = 2(4 - x)=8 - 2x$ and $v = e^{x}$. Then $u'=-2$ and $v' = e^{x}$. So $f'(x)=-2e^{x}+(8 - 2x)e^{x}=(6 - 2x)e^{x}$.
Step2: Find the second - derivative
Again use the product rule. Let $u = 6 - 2x$ and $v = e^{x}$, $u'=-2$ and $v' = e^{x}$. Then $f''(x)=-2e^{x}+(6 - 2x)e^{x}=(4 - 2x)e^{x}$.
Step3: Find the inflection points
Set $f''(x)=0$. Since $e^{x}\gt0$ for all $x\in R$, we solve $4 - 2x = 0$, which gives $x = 2$.
Step4: Test the intervals
Choose a test - point in the interval $(-\infty,2)$, say $x = 0$. Then $f''(0)=(4-2\times0)e^{0}=4\gt0$, so the function is concave upward on $(-\infty,2)$. Choose a test - point in the interval $(2,\infty)$, say $x = 3$. Then $f''(3)=(4 - 2\times3)e^{3}=-2e^{3}\lt0$, so the function is concave downward on $(2,\infty)$.
Answer:
B. The function is concave upward on $(-\infty,2)$. It is concave downward on $(2,\infty)$.